Implementing reworkable strain relief packaging structure for electronic component interconnects

ABSTRACT

A method and structure are provided for implementing enhanced reworkable strain relief packaging for electronic component interconnects. A plurality of custom strain relief pads is provided with a component footprint wiring layout on a component carrier or a component. The custom strain relief pads are disposed at component body perimeter locations. A solder mask is applied around these pad locations to provide a constrained area for a fusible surface coating. A fusible surface coating material is applied in the to the custom strain relief pads in the constrained area and then soldering of components is performed. Then a structural adhesive material is applied to the custom strain relief pad locations.

This application is a divisional application of Ser. No. 15/373,511filed Dec. 9, 2016.

FIELD OF THE INVENTION

The present invention relates generally to the data processing field,and more particularly, relates to a method and structure forimplementing enhanced reworkable strain relief packaging for electroniccomponent interconnects.

DESCRIPTION OF THE RELATED ART

Ever increasing electronic packaging density within computer systems andindustry standard drawer formats typically drives less room formechanical support within system frames, systems drawers, and CentralComputer Electronics (CEC) chassis designs. As a result, electricalinterconnects within these systems possess less structural support andare at greater risk for mechanical damage driven from shock andvibration or other mechanical strain events that arise during electroniccard test operations, systems integration operations, system shipping,data center moves, repair, replacement or upgrade actions, and/or duringoverall in-service operation through time. The scope of strain induceddamage on interconnects typically results in cracked, separated,cratered solder joint interconnects, or cracked copper wiringterminations a solder joint pads, which then drive intermittent or openjoint conditions and latent system field failures.

When sufficient structural support cannot be provided in a system orboard design, a simple way to provide solder joint strain relief and/orstrain reduction on components is to incorporate the use of acommercially available structural “edgebond” or “cornerbond” underfilladhesive. These types of adhesives are designed to be applied toperimeter locations of component bodies and bond the edges of componentbodies to the mounting substrate or circuit board. Unlike full underfilladhesives, these materials are much easier to apply, and have short curetimes. In addition, these materials are designed to have restrictedflow, and fill and bond only to component edges and a very smalldistance (1 mm or less) under the bottom edges of components. When fullycured, these structural adhesives provide outrigger supports oncomponents and provide strain reduction on component solder joints byeither moving high strain fields outside of the component footprint orby simply reinforcing strength of the overall package structure in thepresence of high strains and strain rates. Typical “Edgebond” or“Cornerbond” adhesives are heat cured or UV cured epoxy base materialsthat are filled with inorganic particles to tailor expansion propertiesand materials strength properties. Examples of commercially availablestrain relief materials include products by Zymet of East Hanover, N.J.,Zymet UA2605B (heat cure) and Dymax Corporation of Torrington, Conn.,Dymax 9309SC (UV cure).

The main problem faced by using edge bond and corner bond materials isthat once applied and cured, component rework is not enabled. Somematerials are claimed to be reworkable by their manufacturer, byallowing the component to be removed from the board surface when heat isapplied, but significant post component removal cleanup of residualbonding material must be provided, making the rework process untenablefrom yield, cycle time and overall cost perspectives. In someapplications, this can result in a very significant manufacturing costincrease, especially if custom application specific integrated circuits(ASICs) such as state of the art field programmable gate array (FPGA)module packages or CPU modules and sockets require rework, or if otherconnector or module types require rework on high asset value, complexboard constructions.

A need exists for a method and structure for implementing enhancedreworkable strain relief packaging for electronic componentinterconnects.

As used in the following description and claims, the term componentcarrier should be understood to broadly include a printed wiring board(PWB), a printed circuit board (PCB), circuit carrier, and othersubstrates including an interconnect substrate, and various substratessuitable for the mounting of electronic components.

SUMMARY OF THE INVENTION

Principal aspects of the present invention are to provide a method andstructure for implementing enhanced reworkable strain relief packagingfor electronic component interconnects. Other important aspects of thepresent invention are to provide such method and structure substantiallywithout negative effects and that overcome many of the disadvantages ofprior art arrangements.

In brief, a method and structure are provided for implementing enhancedreworkable strain relief packaging for electronic componentinterconnects. A plurality of custom strain relief pads is provided witha component footprint wiring layout on a component carrier. The customstrain relief pads are disposed at component body perimeter locations. Asolder mask is applied around these pad locations to provide aconstrained area for a fusible surface coating. A fusible surfacecoating material is applied in the to the custom strain relief pads inthe constrained area and then soldering of components is performed. Thena structural adhesive material is applied to the custom strain reliefpad locations.

In accordance with features of the invention, the custom strain reliefpads are disposed at component body perimeter locations, such as atarray type component corners or array type component edge locations.

In accordance with features of the invention, the fusible surfacecoating includes a selected one of solder, other low melt metal, andmetal alloy composition.

In accordance with features of the invention, the solder mask appliedaround the custom strain relief pad locations provides structuraladhesive strain relief material wells.

In accordance with features of the invention, the fusible surfacecoating material is applied via a selected method including one of pastedeposition, wave soldering, hot air solder leveling, plating, and otherphysical and chemical deposition method including one of vapordeposition, and sputtering.

In accordance with features of the invention, the soldering ofcomponents is performed using, for example, a selected one of a surfacemount technology (SMT) component-to-board assembly method and solderreflow method.

In accordance with features of the invention, the structural adhesivematerial includes adhesive strain relief materials, such as ZymetUA2605B (heat cure) and Dymax 9309SC (UV cure).

In accordance with features of the invention, the custom strain reliefpads having strain relief adhesive material dispensed thereon aredesigned to reside partially outside a component body perimeter andpartially underneath a component body to accommodate optimized filletformation of the strain relief adhesive to the custom coated padsurfaces, to the bottom surface face of the component perimeter, and tothe vertical sidewalls of the component perimeter.

In accordance with features of the invention, the fusible layer has acomposition which is designed to melt at or below a melting temperatureof the component solder joints. Local heat is applied to a particularcomponent using conventional rework tools. As a result, melting andliquid layer formation beneath the structural strain relief adhesiveprovides de-bonding, and an easy, clean separation and removal of thecomponent and the strain relief adhesive from the fusible release layercoating present on the custom strain relief pads.

In accordance with features of the invention, the novel packagingstructure enables easy component removal and subsequent site rework andcomponent replacement to be realized when a rigid structural adhesive isused on component corners or edges to ruggedize an assembly and providecomponent strain relief.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention together with the above and other objects andadvantages may best be understood from the following detaileddescription of the preferred embodiments of the invention illustrated inthe drawings, wherein:

FIGS. 1A and 1B, and FIGS. 1C and 1D are respective top and side viewsillustrating example structures for implementing enhanced reworkablestrain relief packaging for electronic component interconnects inaccordance with the preferred embodiments;

FIGS. 2A and 2B and FIGS. 2C and 2D are respective top and side viewsillustrating example structures for implementing enhanced reworkablestrain relief packaging for electronic component interconnects inaccordance with the preferred embodiments;

FIGS. 3A and 3B and FIGS. 3C and 3D are respective top and side viewsillustrating example structures for implementing enhanced reworkablestrain relief packaging for electronic component interconnects inaccordance with the preferred embodiments;

FIGS. 4A and 4B illustrate example package structures and processsequence for implementing enhanced reworkable strain relief packagingfor electronic component interconnects in accordance with the preferredembodiments;

FIGS. 5A and 5B illustrate example package structures and processsequence for implementing enhanced reworkable strain relief packagingfor electronic component interconnects in accordance with the preferredembodiments; and

FIG. 6 illustrates example package structures for implementing enhancedreworkable strain relief packaging for electronic componentinterconnects in accordance with preferred embodiments of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following detailed description of embodiments of the invention,reference is made to the accompanying drawings, which illustrate exampleembodiments by which the invention may be practiced. It is to beunderstood that other embodiments may be utilized and structural changesmay be made without departing from the scope of the invention.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

In accordance with features of the invention, a method and structure areprovided for implementing enhanced reworkable strain relief packagingfor electronic component interconnects. A plurality of custom strainrelief pads is provided with a component footprint wiring layout on acomponent carrier. The custom strain relief pads are disposed atcomponent body perimeter locations. A solder mask is applied aroundthese pad locations to provide a constrained area for a fusible surfacecoating. A fusible surface coating material is applied in the to thecustom strain relief pads in the constrained area and then soldering ofcomponents is performed. Then a structural adhesive material is appliedto the custom strain relief pad locations.

In accordance with features of the invention, a method and structure areprovided for implementing enhanced reworkable strain relief packagingproviding solder ball wear out stress relief. The enhanced reworkablestrain relief packaging structure for electronic component interconnectsenables applying local heat for component removal, rework andreplacement when required due to functional or damage issues, thefusible layer has a composition which is designed to melt at or belowthe melting temperature of the solder joints, providing an easy, cleanseparation of the component and the strain relief adhesive from thefusible release layer.

Having reference now to the drawings, in 1A and 1B, and FIGS. 1C and 1D,there are shown example structures generally designated by referencecharacters 100, 120 for implementing enhanced reworkable strain reliefpackaging for electronic component interconnects in accordance with thepreferred embodiment. Structures 100, 120 include a printed wiring board(PWB) 102 with an example footprint 104 of ball grid array (BGA) modulesor connector components with a plurality of custom corner or edge pads106 shown on PWB 102. In FIGS. 1C and 1D, the structure 120 includes afusible layer 112 extending above and covering the custom corner or edgepads 106, and a fusible layer 114 extending around the custom corner oredge pads 106 in the example footprint 104.

In accordance with features of the invention, the fusible layer 112, 114has a composition which is designed to melt at or below a meltingtemperature of the component solder joints. Local heat is applied to aparticular component using conventional rework tools. As a result,melting and liquid layer formation beneath the structural strain reliefadhesive provides de-bonding, and an easy, clean separation and removalof the component and the strain relief adhesive from the fusible releaselayer coating present on the custom strain relief pads.

In accordance with features of the invention, the novel packagingstructures 100, 120 enable easy component removal and subsequent siterework and component replacement to be realized when a rigid structuraladhesive is used on component corners or edges to ruggedize an assemblyand provide component strain relief.

Referring now to FIGS. 2A and 2B and FIGS. 2C and 2D, there are shownrespective top and side views illustrating example structures generallydesignated by reference char200, 220 for implementing enhancedreworkable strain relief packaging for electronic componentinterconnects in accordance with the preferred embodiments. Structure200 includes a printed wiring board (PWB) 202 with an example overmoldedorganic ball grid array (BGA) module 204 solder attached to PWBcomponent site with a plurality of custom corner or edge pads 206 on PWB202 and below a component laminate 208. In FIGS. 1C and 1D, thestructure 220 includes a printed wiring board (PWB) 202 with an exampleHLGA connectors 212 solder attached to PWB component site with aplurality of custom corner or edge pads 206 on PWB 202 and below acomponent laminate 208.

Referring now to FIGS. 3A and 3B and FIGS. 3C and 3D, there are shownrespective top and side views illustrating example structures generallydesignated by reference characters 300, 320 for implementing enhancedreworkable strain relief packaging for electronic componentinterconnects in accordance with the preferred embodiments. Structures300, 320 illustrate structures 200, 220 including an additional fusiblelayer 302 extending above and covering the custom corner or edge pads206, of structures 200, 220 in accordance with features of theinvention. The additional fusible layer 302 extending above and coveringthe custom corner or edge pads 206 are best seen in FIGS. 3B, and 3D.

FIGS. 4A and 4B respectively schematically illustrate example packagestructures generally designated by reference characters 400, and processsequence steps for implementing enhanced reworkable strain reliefpackaging for electronic component interconnects in accordance with thepreferred embodiments.

Referring now to FIG. 4A and FIG. 4B, package structures are shown inFIG. 4A, and in FIG. 4B, there is shown a flow chart illustratingexample process sequence steps corresponding to the package structuresof FIG. 4A. In FIG. 4A, structure 402 illustrates a board component sitefootprint with array pads and custom pads for strain relief adhesiveattach, and structure 404 illustrates the board component site footprintafter solder paste and fusible layer applications the board componentsite footprint, as indicated at blocks 422 and 424 in FIG. 4B. Structure406 illustrates a component placement onto the site and as indicated atblock 426. Structure 408 illustrates component board assembly aftersolder reflow and component attach and as indicated at block 428.Structure 410 illustrates component board assembly after strain reliefadhesive dispense and cure and as indicated at block 430. Structure 412illustrates component board assembly site undergoing local heating forrework and component removal and as indicated at block 432. Structure414 illustrates component removal after heat application includingrelease of strain relief adhesive from liquid fusible coat present oncustom pads and as indicated at block 434. Structure 416 illustratesboard component site footprint solder redress and as indicated at block436. Structure 418 illustrates new component placement ontoreworked/redressed site and as indicated at block 438. Structure 420illustrates component board assembly after solder reflow and componentattach on the reworked site and as indicated at block 440. Structure 422illustrates new component assembly after strain relief adhesive dispenseand cure on the reworked site and as indicated at block 440.

FIGS. 5A and 5B respectively schematically illustrate example packagestructures generally designated by reference characters 400, and processsequence steps for implementing enhanced reworkable strain reliefpackaging for electronic component interconnects in accordance with thepreferred embodiments.

Referring now to FIG. 5A and FIG. 5B, in FIG. 5A package structures areshown with high magnification of the custom pad area 106, 206, and inFIG. 5B, there is shown a flow chart illustrating example processsequence steps corresponding to the package structures of FIG. 5A. InFIG. 5A, structure 502 illustrates a local custom pad feature atcomponent footprint perimeter for strain relief adhesive attach, and asindicated at block 518. Structure 504 illustrates the local custom padfeature at component footprint perimeter for strain relief adhesiveattach after solder paste and fusible layer application, as indicated ata block 520. Structure 506 illustrates an optional reflowed fusiblerelease layer as indicated at block 522. Structure 508 illustratescomponent board assembly after solder reflow and component attach and asindicated at block 524. Structure 510 illustrates component boardassembly after component solder reflow and attach to board assembly andafter strain relief adhesive dispense and cure as indicated at block524. Note in structure 510 that the bulk of adhesive fillet resides onpad with adhesive material contained within the aperture of the soldermask opening surrounding the pad feature. Structure 512 illustratescomponent board assembly site after component removal for site reworkafter undergoing local heating for rework and component removal and bulkof the adhesive separates cleanly for the liquid fusible layer asindicated at block 528. Structure 514 illustrates rework, reflow and newcomponent attachment after site redress as indicated at block 530.Structure 516 illustrates new component assembly after strain reliefadhesive dispense and cure on the completed reworked site as indicatedat block 534.

Referring now to FIG. 6, there are shown package structures with highmagnification of custom pad areas generally designated by referencecharacters 600, 610, and 620 in accordance with preferred embodiments ofthe invention. Each of the structures 600, 610, and 620 includes acomponent carrier 602, such as a printed wiring board (PWB) 602, and acomponent 604, such as a Ball Grid Array (BGA) component 604.

In structure 600, pad features and fusible release layer 606 areprovided on the PWB 602, such as illustrated and described above. Instructure 610, custom pad features and fusible release layer 612 isprovided on the BGA 604. The custom pad features 612 advantageously areprovided on the bottom body perimeter of the BGA component 604surrounding the array of solder attach balls, and are coated withsimilar release layers of fusible materials described above. The custompad features and fusible release layer 612 are provided on the BGA 604facilitate easily reworking the component as well by allowing for easyremoval of the structural strain relief adhesive from the surface of theBGA component 604. In structure 620, custom pad features and fusiblerelease layer 612 are provided on the BGA 604 as described with respectto structure 610, and custom pad features and fusible release layer 624are provided on the PWB 602, as described above.

While the present invention has been described with reference to thedetails of the embodiments of the invention shown in the drawing, thesedetails are not intended to limit the scope of the invention as claimedin the appended claims.

1. A method for implementing enhanced reworkable strain relief packagingfor electronic component interconnects comprising: providing a componentcarrier; providing a plurality of custom strain relief pads with acomponent footprint wiring layout on the component carrier, said customstrain relief pads disposed at component body perimeter locations;applying a solder mask around said pad locations, said solder maskproviding a constrained area; depositing a fusible surface coatingmaterial to said custom strain relief pads; soldering a component tosaid component carrier; and depositing a structural adhesive material tothe custom strain relief pad locations.
 2. The method as recited inclaim 1 includes forming said fusible surface coating material of aselected material having a melting temperature at or below a meltingtemperature of said component solder, and removing said component forrework and removing said deposited structural adhesive material withlocal heating.
 3. The method as recited in claim 1 includes depositing afusible surface coating material to said custom strain relief pads inthe constrained area.
 4. The method as recited in claim 1 whereinproviding said component carrier includes providing a printed circuitboard (PCB); said printed circuit board (PCB) arranged for mountingelectronic components and formed by a standard PCB manufacturingprocess.
 5. The method as recited in claim 1 wherein providing saidcomponent carrier includes providing a circuit carrier arranged formounting electronic components.
 6. The method as recited in claim 1wherein soldering said component soldered to said component carrierincludes a reflow solder method.
 7. The method as recited in claim 1wherein soldering said component soldered to said component carrierincludes a surface-mount technology (SMT) assembly method.
 8. The methodas recited in claim 1 wherein depositing said structural adhesivematerial to the custom strain relief pad locations includes ultraviolet(UV) curing.
 9. The method as recited in claim 1 wherein depositing saidstructural adhesive material to the custom strain relief pad locationsincludes heat curing.
 10. The method as recited in claim 1 wherein saiddeposited structural adhesive material provides a rigid structuraladhesive, and further includes removing said component and saidstructural adhesive material carried by said fusible surface coatingwith said component by a local heating.
 11. The method as recited inclaim 10 wherein said rigid structural adhesive ruggedizes and providesstrain relief for said component and strain relief for solder joints.12. A method for implementing enhanced reworkable strain reliefpackaging for electronic component interconnects comprising: providing acomponent; providing a plurality of custom strain relief pads on thecomponent disposed at component perimeter locations; applying a soldermask around said pad locations, said solder mask providing a constrainedarea; depositing a fusible surface coating material to said customstrain relief pads; and depositing a structural adhesive material to thecustom strain relief pad locations.
 13. The method as recited in claim12 further includes providing a plurality of second custom strain reliefpads on a component carrier disposed at component perimeter locations,applying a solder mask around said second pad locations, said soldermask providing a second constrained area; depositing a fusible surfacecoating material to said second custom strain relief pads; anddepositing a structural adhesive material to the second custom strainrelief pad locations. 14-20. (canceled)